1. Field of the Invention
The present invention generally relates to a heater for heating a wafer, for example, a heater which is suitable for forming a thin film formed on a semiconductor wafer or a wafer of a liquid crystal display and a circuit board or the like, or for forming a resist film by drying and baking a resist solution applied on the wafer.
2. Description of the Related Art
In forming of a semiconductor thin film, etching, baking of a resist film, etc. in a process for fabricating a semiconductor, there is used a heater made of ceramics for heating a semiconductor wafer (hereinafter, abbreviated as a “wafer”).
A conventional device for fabricating a semiconductor may be classified into a batch mode wherein a plurality of wafers are heated en bloc and a single mode wherein a plurality of wafers are heated one by one. In the single mode, since temperature controllability is excellent, a heater made of ceramics is widely used as a wiring of a semiconductor element gets finer and it is required to enhance accuracy of the heat treatment temperature.
As such the heater made from ceramics, for example, in the following Japanese Patent Kokai No. 2001-203156 or No. 2001-313249, heaters made from ceramics as shown in FIG. 18 are proposed.
This heater 71 is essentially composed of a plate shaped ceramics body 72 and a metal case 79, wherein the metal case 79 is made of a metal such as aluminum, etc. and takes a shape with a bottom. The plate shaped ceramics body 72 is made of nitride ceramic or carbide ceramic. The plate shaped ceramics body 72 is fixed in an opening of the metal case 79 by a bolt 80 with an adiabatic connection member 74 made of a resin interposed therebetween. An upper surface of the plate shaped ceramics body 72 is adapted to serve as a mounted surface 73 on which a wafer W is loaded, and at the same time, a lower surface of the plate shaped ceramics body 72 is adapted to be provided with a concentric circle shaped resistance heating element 75, for example, as shown in FIG. 19.
Moreover, the resistance heating element 75 has a terminal, to which a power supply terminal 77 is brazed. The power supply terminal 77 is electrically connected with a lead 78 that is inserted through a hole 76, wherein the hole 76 is used for drawing out the lead and is formed on a bottom 79a of the metal case 79.
Meanwhile, in the case of such heaters 71, it is important to make temperature distribution of the wafer uniform, in order either to form a homogeneous film throughout the surface of the wafer W or to make a heating reaction of the resist film homogeneous. For this reason, in order to lessen an in-plane temperature difference of the wafer, it has been carried out up to now to adjust resistance distribution of the resistance heating element 75 or to control a temperature of the resistance heating element 75 in a divided manner. However, the resistance heating element fabricated by a printing method has a problem that a film thickness becomes uneven and thus a resistance value is not obtained just as it is designed. So, there is disclosed a method for adjusting the resistance distribution, wherein a channel is formed by use of a laser beam as described in Japanese Patent Kokai No. 2001-244059 No. 2002-141159 or No. 2002-151235 and thereby the resistance is adjusted.
Further, there is a method for corrugating the resistance heating element to trim the corrugated part with a laser, as described in Japanese Patent Kokai No. 2002-043031. As shown in FIG. 10, there is a method for forming a plurality of channels m on an edge of a belt of the resistance heating element by use of a laser, and thereby lessening the in-plane temperature difference of the wafer W by means of the heater whose resistance is adjusted, which is disclosed in Japanese Patent Kokai No. 2002-203666.
However, the in-plane temperature difference of the wafer is lessened, but it is still insufficient to form the homogeneous film throughout the surface of the wafer W. Therefore, it is required a heater capable of more uniformly heating the temperature distribution.